This invention relates generally to microelectromechanical system (MEMS) devices and operating methods therefor, and more particularly to MEMS optical cross-connect (OXC) switches and methods of operating same.
Microelectromechanical systems (MEMS) recently have been developed as alternatives for conventional electromechanical devices, such as relays, actuators, valves and sensors. MEMS devices are potentially low-cost devices, due to the use of simplified microelectronic fabrication techniques. New functionality also may be provided because MEMS devices can be physically much smaller than conventional electromechanical devices.
MEMS technology has been used to fabricate optical cross-connect (OXC) switches that include a plurality of input optical paths, a plurality of output optical paths, and an array of electromechanical optical switches, such as movable reflectors, that selectively move to couple the plurality of input optical paths to the plurality of output optical paths. In particular, MEMS optical cross-connect switches can include an array of n rows and m columns of reflectors on a substrate such as a microelectronic substrate, to reflect optical energy from any of m input optical paths to any of n output optical paths. The selected reflector can be located in the array where the column associated with the m inputs and the row associated with the n outputs intersect. The selected reflector can be placed in a reflecting position to reflect the optical energy from the input to the selected output. The other reflectors can be placed in a non-reflecting position, so as not to impede the propagation of the optical energy from the input to the selected reflector and to the output.
Some conventional MEMS OXC switches operate by orienting the reflectors of the array using magnetic fields. In particular, the reflectors therein may be oriented horizontally (in the plane of the substrate on which the reflectors are located) in a non-reflecting position, and vertically (orthogonal to the substrate) in a reflecting position. Therefore, to switch optical energy from an input of the OXC switch to an output thereof, the selected reflector can be oriented vertically, and other blocking reflectors can be oriented horizontally. Magnetically actuated MEMS OXC switches are described, for example, in U.S. patent application Ser. No. 09/489,264, filed Jan. 21, 2000 (now U.S. Pat. No. 6,396,975), entitled MEMS Optical Cross-Connect Switch, to Wood et al., and assigned to the assignee of the present invention, the disclosure of which is hereby incorporated herein by reference in its entirety, and U.S. patent application Ser. No. 09/487,976, filed Jan. 20, 2000 (now U.S. Pat. N0. 6,366,186), entitled MEMS Magnetically Actuated Switches and Associated Switching Arrays to Hill et al., assigned to the assignee of the present invention, the disclosure of which is hereby incorporated herein by reference in its entirety.
Magnetically actuated optical cross-connect switches also are disclosed in three publications by members of the Berkeley Sensor and Actuator Center (BSAC) of the University of California, Berkeley. In particular, in a publication entitled Magnetic Microactuation of Torsional Polysilicon Structures to Judy et al., Sensors and Actuators A, Vol. 53, 1996, pp. 392-397, a microactuator technology utilizing magnetic thin films and polysilicon flexures is applied to torsional microstructures. These structures are constructed in a batch-fabrication process that combines electroplating with conventional IC-lithography, materials, and equipment. A microactuated mirror made from a 430 xcexcmxc3x97130 xcexcmxc3x9715 xcexcm nickel-iron plate attached to a pair of 400 xcexcmxc3x972.2 xcexcmxc3x972.2 xcexcm polysilicon torsional beams may be rotated more than 90xc2x0 out of the plane of the wafer and actuated with torque greater than 3.0 nN m. The torsional flexure structure constrains motion to rotation about a single axis, which can be an advantage for a number of microphotonic applications (e.g., beam chopping, scanning and steering). See the abstract of this publication.
A 1997 publication entitled Magnetically Actuated, Addressable Microstructures to Judy et al., Journal of Microelectromechanical Systems, Vol. 6, No. 3, September 1997, pp. 249-255, discloses that surface-micromachined, batch-fabricated structures that combine plated-nickel films with polysilicon mechanical flexures to produce individually addressable, magnetically activated devices have been fabricated and tested. Individual microactuator control was achieved in two ways: 1) by actuating devices using the magnetic field generated by coils integrated around each device and 2) by usingo electrostatic forces to clamp selected devices to all insulated ground plane while unclamped devices are freely moved through large out-of-plane excursions by an off-chip magnetic field. The disclosed application for these structures is micromirrors for microphotonic systems where they can be used either for selection from an array of mirrors or else individually for switching among fiber paths. See the abstract of this publication. Moreover, this publication discloses, at Page 253, four advantages of using electrostatic forces (instead of using integrated coils), to achieve individual microactuator control. These advantages include the following:
1) Arrays of elements can be readily addressed using well-known digital-memory address techniques.
2) The clamping scheme is easily incorporated in a batch-fabrication process.
3) Clamping is accomplished with very little increase in the area of an array in contrast to that needed for on-chip coils.
4) Although power is required to generate the magnetic field necessary to move unclamped devices, no static power is needed to clamp devices. An array of devices that could be clamped in the up position as well as the down position, would only need power to generate the magnetic field necessary to change the up-down configuration of the matrix.
Finally, a 1998 publication entitled Magnetically Actuated Micromirrors for Fiber-Optic Switching to Behin et al., Solid-State Sensor and Actuator Workshop, Hilton Head Island, S.C., Jun. 8-11, 1998, pp. 273-276, describes the design, fabrication and operation of magnetically actuated micromirrors with electrostatic clamping in dual positions for fiber-optic switching applications. The mirrors are actuated by an off-chip electromagnet and can be individually addressed by electrostatic clamping either to the substrate surface or to the vertically etched sidewalls formed on a top-mounted (110)-silicon chip. This publication shows the positioning accuracy inherent in this approach makes it suitable for Nxc3x97M optical switches. See the abstract of this publication.
Other actuation techniques may be used to orient the reflectors of the array. For example, application Ser. No. 09/542,170, filed Apr. 5, 2000 (now U.S. Pat. No. 6,445,842), entitled Microelectromechanical Optical Cross-Connect Switches Including Mechanical Actuators and Methods of Operating Same to Dhuler et al., and assigned to the assignee of the present invention, the disclosure of which is hereby incorporated herein by reference in its entirety, discloses MEMS OXC switches having mechanical actuators. In particular, the MEMS OXC switches can include a plurality of reflectors, wherein each of the plurality of the reflectors is movable to at least one of a respective first reflector position along a respective optical beam path from an associated input of the MEMS OXC switch to an associated output thereof and a respective second reflector position outside the optical beam path. A mechanical actuator moves to at least one of a first mechanical actuator position and a second mechanical actuator position. A selector selects ones of the plurality of reflectors to be coupled to the mechanical actuator and at least one of the plurality of reflectors to be decoupled from the mechanical actuator, wherein the mechanical actuator is coupled to the selected ones of the plurality of reflectors in the first actuator position and wherein the mechanical actuator moves the selected ones of the plurality of reflectors from the respective first reflector positions to the respective second reflector positions when the mechanical actuator moves from the first mechanical actuator position to the second mechanical actuator position. See the abstract of this patent application.
As the size of optical cross-connect switches continues to increase, it may become increasingly difficult to provide the requisite space for the control lines that control the switching of the individual electromechanical optical switches such as movable reflectors. In particular, in order to allow selection of an individual optical switch, a separate control line generally is provided for each switch. Thus, for an nxc3x97n array of movable reflectors, n2 control lines may be needed. As the size of OXC devices increase, for example up to 1024xc3x971024 arrays of reflectors or larger, up to one million or more control lines may be needed to individually address each reflector. These control lines may occupy significant area in the OXC device.
This area may be particularly excessive in MEMS OXC devices, wherein a single microelectronic substrate preferably contains the input optical paths, the output optical paths, the array of electromechanical optical switches and the individual control lines. Moreover, in an integrated circuit OXC device having four edges, the input optical paths and the output optical paths generally are provided on two adjacent edges and a pass-through output optical path generally is provided on a third edge opposite the input optical paths. This may allow only one edge to remain for electrical input/output connections. Even if up to one million or more individual control lines could be formed on a microelectronic substrate, it may be difficult to provide up to one million or more input/output connections on one edge of the microelectronic substrate.
Optical cross-connect switches according to embodiments of the present invention include a plurality of input optical paths, a plurality of output optical paths, and an array of electromechanical optical switches such as movable reflectors that are arranged in a plurality of rows of the electromechanical optical switches and a plurality of columns of the electromechanical optical switches, and that selectively move to couple the plurality of input optical paths to the plurality of output optical paths. A plurality of row address lines also are provided, a respective one of which is electromagnetically (i.e. electrically and/or optically) coupled to a respective row of the electromechanical optical switches. A plurality of column address lines also are provided, a respective one of which is electromagnetically coupled to a respective column of the electromechanical optical switches.
In embodiments of the invention, the electromechanical optical switches are configured to be selected upon selection of the respective row address line and column address line, but not to be selected upon selection of fewer than both (neither or only one) of the respective row address line and column address line. In other embodiments, the electromechanical optical switches are configured to be selected except for an electromechanical optical switch that is electromagnetically coupled to the respective row address line and column address line. In yet other embodiments, the plurality of input optical paths, the plurality of output optical paths, the array of electromechanical optical switches, the plurality of row address lines and the plurality of column address lines are on a microelectronic substrate, such as a silicon semiconductor substrate.
Optical cross-connect switches according to embodiments of the invention can provide a first plurality of electromechanical optical switches such as movable reflectors that selectively move to couple a plurality of input optical paths to a plurality of output optical paths. These embodiments of optical cross-connect switches also include a second plurality of electromagnetic control lines that are less than the first plurality and that are selectively electromagnetically coupled to the first plurality of electromechanical optical switches, to control the selective movement thereof. Thus, for example, if there are n2 electromechanical optical switches that couple n input optical paths to n output optical paths, less than n2 electromagnetic control lines may be provided. In other embodiments, the number of electromagnetic control lines is proportional to the number of rows plus the number of columns. Thus, 2n control lines, or a number of control lines that is proportional to 2n but less than n2, may be provided.
In other embodiments of optical cross-connect switches according to embodiments of the present invention, each of the electromechanical optical switches includes a first electrode and a second electrode. A respective first electrode is electromagnetically coupled to a respective row address line and a respective second electrode is electromagnetically coupled to a respective column address line. In some embodiments, the electromechanical optical switches are configured such that activation of both the first and second electrodes by the respective row and column lines allows movement of the respective electromechanical optical switch, but activation of fewer than both of the first and second electrodes prevents movement of the respective electromechanical switch. In other embodiments, the electromechanical optical switches are configured such that activation of both the first and second electrodes by the respective row and column lines prevents movement of the respective electromechanical optical switch, but activation of fewer than both of the first and second electrodes allows movement of the respective electromechanical optical switch.
In yet other embodiments, the electromechanical optical switches each include a reflector that is movable between first and second positions, wherein the reflector can move from the first position to the second position when both the first and second electrodes are activated and are clamped in the first position otherwise. In some embodiments, the first and second clamping electrodes are attached to and move with, the reflector. In other embodiments, the electromechanical optical switches each includes a reflector that is movable between first and second positions, wherein the first electrodes are attached to and move wit the reflector and wherein the second electrodes are detached from and do not move the reflector.
In still other embodiments of the present invention, each of the electromechanical optical switches includes an electronic switch that is electrically coupled to the respective row and column line. In some embodiments, the electronic switch comprises a transistor, such as a field effect transistor having a controlling electrode such as a gate, and a pair of controlled electrodes, such as source and drain electrodes. The controlling electrode is electrically connected to one of the respective row and column line and one of the controlled electrodes is electrically connected to the other of the respective row and column line.
Embodiments of the present invention may be used with global actuators that apply a global actuation force to the array of electromechanical optical switches. The global actuator can apply a global electrostatic, magnetic, mechanical and/or other actuation force to the array of electromechanical optical switches.
Embodiments of the invention can include a plurality of input optical paths, a plurality of output optical paths, and an array of movable reflectors that are arranged in a plurality of rows of the movable reflectors and a plurality of columns of the movable reflectors. The movable reflectors selectively move between a first position that is outside the input optical paths, and a second position along at least one of the input optical paths. Each of the movable reflectors includes a first movable electrode and a second movable electrode that are attached thereto and move therewith.
A plurality of row address lines also are included, a respective one of which is electrically coupled to the first movable electrodes in a respective row of the movable reflectors. A plurality of column address lines also is included, a respective one of which is electrically coupled to the second movable electrodes in a respective column of the movable reflectors. A first clamp electrode also may be included that is adjacent the first position of the movable reflectors. A second clamp electrode also may be included that is adjacent the second position of the movable reflectors. The plurality of input optical paths, the plurality of output optical paths, the array of movable reflectors, the plurality of row address lines, the plurality of column address lines and the first clamp electrode may be included on a first substrate, such as a first microelectronic substrate. A second clamp electrode may be included on a second substrate, such as a second microelectronic substrate, that is spaced apart from and faces the first substrate.
A global magnetic actuator also may be included that applies a global magnetic actuation force to the array of movable reflectors that can move the reflectors from the first position to the second position. These embodiments may be operated by applying a predetermined voltage to the clamp electrode, a selected row address line and a selected column address line, to thereby cause the movable mirror that corresponds to the selected row address line and the selected column address line to move from the first position towards the second position in the presence of the global magnetic field. More specifically, a predetermined voltage is applied to the first clamp electrode, a selected row address line and a selected column address line, while simultaneously applying the global magnetic actuation force to the array., to thereby cause the movable mirror that corresponds to the selected row address line and the selected column address line to move from the first position toward the second position. The predetermined voltage then may be removed from the selected row address line and the selected column address line, while simultaneously applying the global magnetic actuation force to the array, the thereby clamp the movable mirror that corresponds to the selected row address line and the selected column address line to the second clamp electrode in the second position.
In other embodiments of optical cross-connect switches according to embodiments of the present invention, each of the movable reflectors includes a movable electrode that is attached thereto, and moves therewith, and a fixed electrode adjacent the first position that is detached from the movable reflector and does not move therewith. A respective one of the row address lines is electrically coupled to the fixed electrodes in the respective row of the movable reflectors, and a respective column address line is electrically coupled to the movable electrodes in a respective column of the movable reflectors. A clamp electrode also may be provided that is adjacent the second position of the movable reflectors. The plurality of input optical paths, the plurality of output paths, the array of movable reflectors, the plurality of row address lines, the plurality of column address lines and the fixed electrodes may be on a first substrate such as a microelectronic substrate, and the clamp electrode may be on a second substrate, such as a microelectronic substrate, that is spaced apart and faces the first substrate. A global magnetic actuator also may be provided.
In methods of operation of these embodiments of the invention, a predetermined voltage is applied to a selected row address line and a selected column address line, to thereby cause the mirror that corresponds to the selected row address line and the selected column address line to move from the first position toward the second position in the presence of the global magnetic field. More specifically, a predetermined voltage is applied to a selected row address line and a selected column address line, while simultaneously applying the global magnetic actuation force to the array, to thereby cause the movable mirror that corresponds to the selected row address line and the selected column address line to move from the first position toward the second position. Then, second and third voltages are applied to the selected row address line and the selected column address line, respectively, while simultaneously applying the global magnetic actuation force to the array to thereby clamp the movable mirror that corresponds to the selected row address line and the selected column address line to the clamp electrode in the second position.
Embodiments of the present invention also include electromechanical switch systems that selectively couple electrical inputs and outputs rather than optical inputs and outputs. Thus, an array of electromechanical switches are arranged in a plurality of rows of the electromechanical switches and a plurality of columns of the electromechanical switches, and selectively move to couple the plurality of inputs to the plurality of outputs. A plurality of row address lines and a plurality of column address lines are provided. A substrate also is provided, wherein the plurality of inputs, the plurality of outputs, the array of electromechanical switches, the plurality of row address lines and the plurality of column address lines are on the substrate. The switches may be configured to be selected in the various embodiments that were described above. Thus, electromechanical switching systems may be provided on a single substrate, such as microelectronic substrate, including and column address lines. Accordingly, the number of control lines may be reduced, as was described above.